Methoxyacetic acid is an important intermediate. It is the starting material of the methoxyacetylation, namely the methoxy acetyl chloride is prepared from methoxyacetic acid, which is used in the manufacturing of plant protecting agent and pharmaceuticals. The compound can also be used as plasticizer and coloring agent, as auxiliary agent in the textile industry, and also as a flotation adjuvant.
Several processes are known for preparing methoxyacetic acid. Among these processes the following ones using monochloroacetic acid and the salt thereof as well as methanol are mentioned:
U.S. Pat. No. 2,458,741 (1949) describes a process according to which monochloro acetic acid and methanol are boiled in an autoclave for 4 hours at 200.degree. C., when a mixture of methoxyacetic acid, methyl chloride and dimethyl ether is obtained. Yield for methoxyacetic acid is 35%.
According to German Federal Republic patent No. 2,759,169 (1979) monochloro acetic acid sodium salt, methanol, and sodium methylate are boiled for 2 hours at 75.degree. C. then the reaction mixture is evaporated to dryness. The residue is dissolved in water, acidified with hydrochloric acid then the water is distilled off. Thereafter toluene is added to the reaction mixture and the remaining water and the excess of hydrochloric acid are distilled off. Sodium chloride is filtered hot then washed with toluene. The toluene solutions are combined and fractionated by distillation. After distilling toluene the methoxyacetic acid is purified by vacuum distillation. Yield: 85%. Disadvantages of the process are as follows:
the starting material is monochloroacetic acid sodium salt has to be prepared by a separate process; PA0 after finishing the reaction the excess of methanol has to be distilled off, water is added to the sodium methylate and it is acidified with hydrochloric acid, then the water is distilled off. Methanol is formed from sodium methylate as a result of acidification, and in a hydrochloric acidic medium this results in ester formation with methoxyacetic acid. This compound has to be separated from water, hydrochloric acid and methoxyacetic acid; PA0 also methoxyacetic acid is distilled off together with water, and this is difficult to recover; PA0 dissolved sodium chloride is always present in the system due to the aqueous medium. This causes problems during distillation due to separation in the boiler.